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Old 08-04-2014, 11:36 AM
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Default Antenna Help: Lucas County CQPSK

Attached is a photo of the monster antenna I purchased in order to TRY to obtain a usable signal from the 12 tower Toledo Lucas County / NW OHIO Public Safety P25 trunked system. You can see how large the antenna is with my PRO96 laying on the ground by it. Question: I assume vertical polarization, but I stood outside holding this monster, trying to aim it at only one tower, and I still was getting decode readings of 56%, 42%, 0%, 73%, 33%, 0%, 54% etc... so it is still doing the 'crash and burn' on digital decode.
So I'm looking for suggestions as far as mounting and orientating this antenna for reception of the Lucas NW OH system on the PRO96. Thanks,
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Old 08-04-2014, 2:09 PM
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It looks like you have a reflector with a rubber duck type antenna lashed to the antenna feed point. That configuration probably won't give you the results you expected. It would be better to use the correct driven element with that reflector. Also a directional antenna may or may not help in improving simulcast distortion.
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Old 08-04-2014, 3:59 PM
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Quote:
Originally Posted by johnnyelectron View Post
Attached is a photo of the monster antenna I purchased in order to TRY to obtain a usable signal from the 12 tower Toledo Lucas County / NW OHIO Public Safety P25 trunked system. You can see how large the antenna is with my PRO96 laying on the ground by it. Question: I assume vertical polarization, but I stood outside holding this monster, trying to aim it at only one tower, and I still was getting decode readings of 56%, 42%, 0%, 73%, 33%, 0%, 54% etc... so it is still doing the 'crash and burn' on digital decode.
So I'm looking for suggestions as far as mounting and orientating this antenna for reception of the Lucas NW OH system on the PRO96.
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Originally Posted by WA0CBW View Post
It looks like you have a reflector with a rubber duck type antenna lashed to the antenna feed point. That configuration probably won't give you the results you expected. It would be better to use the correct driven element with that reflector. Also a directional antenna may or may not help in improving simulcast distortion.
BB
And, the driven element probably isn't the right distance from the reflector; I suspect that's a TV antenna which is "optimized" (such as it is) for the frequencies between 470 and 670 MHz, give or take several MHz. The optimum point for 800 MHz is likely a few inches closer to the reflector.

Try the factory driven element first (if it has one), but also experiment by moving your DIY feedpoint closer to the dish.

In answer to your other question, you want vertical polarization.
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Old 08-05-2014, 3:19 PM
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If that reflector is a true parabolic then the focus point will be the same regardless of frequency, Tom. But you are right in that the RS 800 rubber duck is not going to be the best antenna to use with it.

John, you don't say where you are located. But if you are outside of Lucas county then that antenna isn't going to help you. The beam width will be pretty narrow but the signal strength from one or more towers is going to over ride each other and confuse your scanner. You might be better off to reduce your antenna efficiency to the point where you only receive one tower. I live in Delta and I can't get a good copy on that system either.
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Old 08-05-2014, 4:03 PM
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Jack, I'm located in the City of Toledo around St. Anne's Hospital.
What I've tried to do is to 'aim' it to get only one tower, like Station 18, or Flower Hospital temporarily using the cell antenna. I do plan on running coax to the little chunk of square metal at the focal point of the 'dish', but also realize potential cable losses at 850MHz will become an issue.

I didn't know if the new Uniden Home Patrols have solved the simulcast issues or if you need a 'true-blue Motorola' radio to ever get 90% reception that you want? Can you even buy a Moto radio (like you could the Maxtrac on the old system) and get it programmed to scan your talkgroups of interest?
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Old 08-05-2014, 8:35 PM
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The short answer is no, you cannot get a Moto radio to use to listen to the system. Any scanner newer than the Pro96 will handle the simulcast issues better, but none are perfect.
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Old 08-07-2014, 8:48 PM
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If you want a directional antenna try making one of these. It'll likely be far better than a rubber duck Asa driven element. Help me with my homebrew 800MHz Yagi

Note the suggestions in that thread.
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Old 08-08-2014, 8:59 PM
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John, your parabolic reflector with a good 1/2 wave antenna will have a better front to back ratio than a yagi so it should work a little better. I'm using both a Uniden 996T and a GRECOM PSR800. Neither works very well on simulcast systems, they don't have any way to correct missed frames or even missed bits.

You will need to mount the antenna at the focus of the reflector. Then experiment with pointing it in different directions, Maybe you can null out the interfering tower but I wouldn't be too disappointed if you still don't get a good decode on that system.
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Old 08-09-2014, 11:54 PM
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Default Psr 800 works fine

But just like in real estate, the most important thing is :

LOCATION ! LOCATION ! LOCATION !

I am in Euclid and listen to three simulcast systems with no problems.

The trick is not always high gain ( I use the stock "rubber duck")

The key is to just listen to ONE site.

In my case I listen to three systems located on two towers
( one on one and two on the other)
I am two miles from one and two and a half miles from the other.

Pick the closest site, build ( or buy) an attenuator, add attenuation until you
problem "goes away".

This may actually be cheaper then playing with antennas.

Don
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Old 08-13-2014, 7:47 AM
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Don, I'm glad your 800 works well on simulcast. I'm beginning to think that there is a problem with Lucas county's controller. I monitor Fulton county's 700 MHz system which is a stand-all system with a single tower located in Wauseon that uses Lucas county's controller. There are times when I'm lucky to get a good decode 70% of the time and it isn't just me, the dispatcher and/or mobile units will ask for repeats. It seems to have gotten worse since they've added Wood county but that maybe just my imagination. I'm wondering if the controller is overloaded and can't keep up with the workload and that's the root cause. I'm going to have to take a day trip to Bowling Green and see if they have the same problem.
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Old 08-13-2014, 8:47 AM
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Some of the problems everyone is having with their scanners on simulcast trunking systems just might be the way the trunking system has been set up, the antennas the trunking system is using and the audio timing delays the techs have set up at each tower location. These all come into play on how well the radio signals are received out in the field.

Setting up a multi site, simulcast trunking system takes considerable skill. I haven't run into that many techs that seem to have those skills. Not only do all the transmitters need to be exactly on the same frequency, the audio delays at each site need to be in alignment so as not to cause distortion on the received signal. This is why they use GPS receivers at each trunking tower to maintain the frequency stability of the transmitters.

The big areas of concern are in the overlap region of coverage from the different transmitter sites. This audio distortion is called TDI or "Time Delay Interference" in the signal. Not only does this effect how well your scanner will function, but it also effects how well the user radios work on the trunking system.

If the TDI gets out of hand, the users out in the field will have trouble hearing the trunking system. You might think that their radios are wonder devices that will work under all conditions. But they are not science fiction devices out of a Buck Roger's movie. They are just commercial radios that need help in receiving the trunking system just like your scanners.

One of the more recent agencies that just went through an update to their antenna system and adjustment to the TDI was Mobile County, AL. They changed out the antennas and pointed them in different directions on the simulcast portion of their system than what was there before. After the work was completed, the feedback from users in the field was very positive. They could now use their radios in locations that before were either dead or garbled.
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Old 08-13-2014, 5:07 PM
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Quote:
Originally Posted by jackj View Post
Don, I'm glad your 800 works well on simulcast. I'm beginning to think that there is a problem with Lucas county's controller. I monitor Fulton county's 700 MHz system which is a stand-all system with a single tower located in Wauseon that uses Lucas county's controller. There are times when I'm lucky to get a good decode 70% of the time and it isn't just me, the dispatcher and/or mobile units will ask for repeats. It seems to have gotten worse since they've added Wood county but that maybe just my imagination. I'm wondering if the controller is overloaded and can't keep up with the workload and that's the root cause. I'm going to have to take a day trip to Bowling Green and see if they have the same problem.
I'm not sure why you would go to Bowling Green, there are no sites in Wood County and nobody in that part of the county uses this system.

I believe that Fulton County's issue is that one site in not enough to cover a county that size. Users of the Lucas County portion of the system have no issues and have been happy with the system.
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Old 08-13-2014, 6:30 PM
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I really don't know what the problem is with Fulton county's system. Although I'm not being paid to solve their problem I am curious and that's why I'd take a day trip to Bowling Green. As for nobody in that portion of the county on the system, well, maybe not but th Northwest Ohio Regional Public Safety System sure has issued a lot of talkgroups for county agencies. Most of which are based in BG.
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Old 08-13-2014, 7:04 PM
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They may have talkgroups on the system but they are not used. Only agencies in the northern part of the county use the system. I can tell you that you will not have good results in BG with a scanner on the system. I have tried many times with poor results.
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Old 08-13-2014, 7:12 PM
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Looking further, I think the issue in Fulton County is that the only site covering the entire county is only licensed for 85 watts power. That doesn't seem like that would cover over 400 square miles. In Lucas County 8 sites are licensed for 100 watts and the 4 in the City of Toledo are licensed for 70 watts.
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Old 08-13-2014, 7:27 PM
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The antenna you have appears to be a grid antenna for mmds, 2.5 ghz, minus the feed assembly. It is a slice of a parabolic dish.
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Old 08-13-2014, 7:28 PM
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Sorry on closer inspection the feed assembly is there, but it is tuned for 2.5 GHZ.
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Old 08-13-2014, 11:01 PM
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Quote:
Originally Posted by ctpd845 View Post
Looking further, I think the issue in Fulton County is that the only site covering the entire county is only licensed for 85 watts power. That doesn't seem like that would cover over 400 square miles. In Lucas County 8 sites are licensed for 100 watts and the 4 in the City of Toledo are licensed for 70 watts.
But you're forgetting about antenna system gains/losses. Every 3dBi gain basically doubles the power, so a 40 watt transmitter into a 3dBi gain antenna equals 80 watts. Subtract transmission line losses of around 1dB per 100 feet (assuming 1.25" line, which is pretty standard for 700/800 MHz), and you get about 63 watts.

It's actually a little more involved, but that's the basics in a nutshell.

You would be surprised what a single site can cover, especially in flat terrain like NW Ohio.
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Old 08-14-2014, 11:04 AM
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Tom is correct about the coverage. I don't know of any reason why one tower couldn't cover the entire county. Toledo uses a bunch of sites to get coverage inside hi-rise steel-framed buildings, there are a few steel-frame buildings in Fulton county but they are not hi-rise so the framing isn't as strong (read close) as Toledo's 10+ story buildings. I am able to pickup Fulton county's signal in Toledo (around 30 miles) as well as Defiance. The signal is spotty though.
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